Standby biasing of electrochemical sensor to reduce sensor stabilization time during measurement

Abstract

An eye-mountable device includes an electrochemical sensor embedded in a polymeric material configured for mounting to a surface of an eye. The electrochemical sensor applies a stabilization voltage between a working electrode and a reference electrode to allow the amperometric current to stabilize before powering measurement electronics configured to measure the amperometric current and communicate the measured amperometric current. The electrochemical sensor consumes less power while applying the stabilization voltage than during the measurement. The measurement is initiated in response to receiving a measurement signal at an antenna in the eye-mountable device.

What is claimed is: 
     
       1. A method comprising:
 applying a stabilization voltage between a working electrode and a reference electrode in an eye-mountable device, wherein the stabilization voltage is sufficient to cause an analyte to undergo an electrochemical reaction at the working electrode; 
 while the stabilization voltage is being applied, wirelessly receiving a measurement signal at an antenna in the eye-mountable device; 
 responsive to receiving the measurement signal, activating measurement electronics in the eye-mountable device to transition the measurement electronics from a standby mode to an active mode, wherein the measurement electronics consume more power in the active mode than in the standby mode; and 
 during the active mode, operating the measurement electronics to (i) measure an amperometric current through the working electrode, wherein the amperometric current is related to the analyte, and (ii) wirelessly communicate the measured amperometric current via the antenna. 
 
     
     
       2. The method according to  claim 1 , further comprising:
 after wirelessly communicating the measured amperometric current via the antenna, de-activating the measurement electronics to transition the measurement electronics from the active mode to the standby mode. 
 
     
     
       3. The method according to  claim 1 , further comprising intermittently activating the measurement electronics to wirelessly communicate a series of amperometric current values measured through the working electrode, wherein each of the amperometric current values is measured following a stabilization period during which the stabilization voltage is applied to allow current through the working electrode caused by the stabilization voltage to reach a stable value prior to measurement. 
     
     
       4. The method according to  claim 3 , wherein the measurement electronics are intermittently activated with a duty cycle of less than 10 percent. 
     
     
       5. The method according to  claim 1 , further comprising:
 during the active mode, applying a measurement voltage between the working electrode and the reference electrode, wherein the measurement voltage generates the amperometric current. 
 
     
     
       6. The method according to  claim 5 , wherein the stabilization voltage is supplied by an auxiliary power supply and the measurement voltage is supplied by a primary power supply. 
     
     
       7. The method according to  claim 5 , wherein the stabilization voltage and the measurement voltage are approximately equal. 
     
     
       8. The method according to  claim 5 , wherein the stabilization voltage is within 20 percent of the measurement voltage. 
     
     
       9. The method according to  claim 1 , further comprising:
 during the active mode, harvesting energy from radio frequency (RF) radiation received at the antenna to power the measurement electronics. 
 
     
     
       10. The method according to  claim 1 , further comprising:
 applying the stabilization voltage during a stabilization period, wherein the stabilization period has a duration sufficient to allow current through the working electrode to reach a stable value prior to activating the control electronics such that the amperometric current measured by the measurement electronics is not affected by transient variations. 
 
     
     
       11. The method according to  claim 1 , wherein the received measurement signal includes radio frequency radiation for powering an energy harvesting power supply, and wherein the method further comprises:
 rectifying electrical signals on the antenna caused by the received radio frequency radiation to thereby generate a supply voltage; and 
 applying the generated supply voltage to the measurement electronics to power the measurement electronics. 
 
     
     
       12. The method according to  claim 1 , further comprising:
 prior to receiving a subsequent measurement signal, operating the measurement electronics in the active mode to measure a second amperometric current value through the working electrode and wirelessly communicate the second amperometric current value via the antenna. 
 
     
     
       13. A method comprising:
 during a stabilization period, wirelessly transmitting, by a reader, a stabilization signal to an eye-mountable device comprising a working electrode, stabilization electronics, measurement electronics, and an antenna, wherein the stabilization signal is configured to cause the stabilization electronics to apply a stabilization voltage between the working electrode and the reference electrode, wherein the stabilization voltage is sufficient to cause an analyte to undergo an electrochemical reaction at the working electrode; 
 during a measurement period following the stabilization period, wirelessly transmitting, by the reader, a measurement signal to the eye-mountable device, wherein the measurement signal is configured to (i) cause the measurement electronics to measure an amperometric current through the working electrode, wherein the amperometric current is related to the analyte, (ii) cause the measurement electronics to wirelessly communicate the measured amperometric current via the antenna, and (iii) supply power for powering the measurement electronics; and 
 receiving, by the reader, an indication of the measured amperometric current wirelessly communicated from the eye-mountable device. 
 
     
     
       14. The method according to  claim 13 , further comprising:
 during an idle period following the measurement period, the reader discontinuing transmission of wireless signals to the eye-mountable device. 
 
     
     
       15. The method according to  claim 13 , further comprising:
 obtaining, by the reader, a series of amperometric current values wirelessly communicated from the eye-mountable device, by:
 transmitting a stabilization signal to the eye-mountable device to cause the stabilization electronics to apply the stabilization voltage between the working electrode and the reference electrode; 
 transmitting a measurement signal to the eye-mountable device to cause the measurement electronics to measure an amperometric current through the working electrode and wirelessly communicate the measured amperometric current; and 
 receiving, at the reader, an indication of the measured amperometric current; and 
 
 wherein each transmission of the measurement signal immediately follows a transmission of the stabilization signal such that each of the series of amperometric current values is measured following a stabilization period during which the stabilization voltage is applied between the working electrode and the reference electrode to allow current through the working electrode caused by the stabilization voltage to reach a stable value prior to measurement. 
 
     
     
       16. The method according to  claim 15 , wherein the measurement signal is transmitted with a duty cycle of less than 10 percent. 
     
     
       17. The method according to  claim 13 , further comprising:
 receiving, by the reader, an indication of a second measured amperometric current obtained during the measurement period; and 
 comparing the values of the two measured amperometric currents.